Methods for cleaning microelectronic structures with cyclical phase modulation

ABSTRACT

A method of cleaning and removing water, entrained solutes and particulate matter during a manufacturing process from a microelectronic device such as a resist-coated semiconductor substrate, a MEM&#39;s device, or an optoelectronic device comprising the steps of: (a) providing a partially fabricated integrated circuit, MEM&#39;s device, or optoelectronic device having water and entrained solutes on the substrate; (b) providing a densified (e.g., liquid or supercritical) carbon dioxide cleaning composition, the cleaning composition comprising carbon dioxide and, optionally but preferably, a cleaning adjunct; (c) immersing the surface portion in the densified carbon dioxide drying composition, and subjecting the densified carbon dioxide drying composition to cyclical phase modulation during at least a portion of the immersing step to thereby facilitating cleaning; and then (d) removing the cleaning composition from the surface portion. Process parameters are preferably controlled so that the drying composition is maintained as a homogeneous composition during the immersing step, the removing step, or both the immersing and removing step, without substantial deposition of the drying/cleaning adjunct or entrained solutes on the substrate.

RELATED APPLICATIONS

This application is a continuation-in-part of commonly owned,application Ser. No. 09/932,063, filed Aug. 17, 2001 now allowed, whichin turn claims the benefit of Provisional Application Ser. No.60/269,026, filed Feb. 15, 2001, the disclosures of both of which areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention concerns methods and apparatus for removing waterand aqueous-borne solutes from substrates such as semiconductorsubstrates, MEM's, or optoelectronic devices with liquid orsupercritical carbon dioxide

BACKGROUND OF THE INVENTION

Production of integrated circuits, microelectronic devices, andmicro-electro mechanical devices, (MEM's) involve multiple processingsteps many of which incorporate water as either a carrier of chemistry,or a media to facilitate the removal of process byproducts. Theevolution of materials and processes has been lead by a drive towardsmaller feature sizes and more complex microdevices. In some cases, theuse of water in these evolving processes has resulted in challengeswhereby deleterious effects of water and byproducts carried by waterhave been seen. The unique physical properties of dense carbon dioxidein a liquid or supercritical state are of particular interest inpreventing certain of these pitfalls.

One such process where dense CO₂ is of practical application relates toprevention of surface tension or capillary force induced image collapse.This is of particular interest during the aqueous development ofmicro-lithographic images using photoresists. Photoresists arephotosensitive films used for transfer of images to a substrate. Acoating layer of a photoresist is formed on a substrate and thephotoresist layer is then exposed, through a photomask or by othertechniques, to a source of activating radiation. Exposure to activatingradiation provides a photoinduced chemical transformation of thephotoresist coating to thereby transfer the pattern of the photomask (orother pattern generator) to the photoresist coated substrate. Followingexposure, the photoresist is developed to provide a relief image thatpermits selective processing of a substrate. See. e.g., U.S. Pat. No.6,042,997.

A photoresist can be either positive-acting or negative-acting. Fornegative acting resists, the solubility of the exposed region isdecreased such that it remains on the wafer during development while thenon-exposed region is removed. For positive acting resists thesolubility of the exposed region increases in the developer solution, soit is removed during the development step leaving the unexposed regionunaffected. Positive and negative acting resist materials typicallyincorporate chemical functionality that undergoes a transformation uponexposure to UV light at a given wavelength. The transformation is oftenreferred to as a “polarity switch” because polymer polarity increases ordecreases are often the driving force for changes in the solubility ofthe polymer in the developing solution. This transformation isfacilitated by the incorporation of photoacid generators (PAG's) orphotobase generators (PGB's) into the resist compositions. The acid andbase moieties are typically generated upon exposure to the appropriatesource of radiation followed by heat. The developer solutions aretypically aqueous, and are typically dried from the substrate beforefurther processing.

Capillary forces present in the aqueous drying of imaged resist patternscan result in resist deformation and pattern collapse. This problembecomes particularly serious as lithography techniques move towardsmaller image nodes with larger aspect ratios. Researchers havesuggested that collapse problems associated with aqueous drying willaffect the 130-nm technology node, and will become more prevalent insubsequent technologies as aspect ratios increase.

Researchers at both IBM and NTT have suggested that the use of carbondioxide in supercritical resist drying (SRD) may reduce image collapseand film damage. See, e.g., H. Namatsu, J Vac. Sci. Technol. B 18(6),3308-3312 (2000); D. Goldfarb et al., J Vac. Sci. Technol B. 18(6)3313-3317 (2000). However, while the absence of surface tension and theaccessible critical temperature and pressure of CO₂ have been touted aspositives factors for this drying approach, the relatively lowsolubility of water in the supercritical phase has also been describedas a challenge that may necessitate the use of chemical adjuncts toincrease the transport capacity of the fluid. Researchers at IBM and NTThave demonstrated the use of certain surfactants in supercriticalfluid-aided drying. However, the surfactant is described as beingincorporated into a hexane pre-rinse in “indirect SRD” See, e.g.,Goldfarb et al., supra, or only particular surfactants have beenincorporated into the carbon dioxide in “direct SRD”. In both the directand indirect drying methods the choice of surfactants and co-solvents islimited by what is described as compatibility issues leading to resistdamage. Accordingly, there remains a need for new approaches to SRDusing carbon dioxide.

Another problem with drying of surfaces on microelectronic substrates(e.g. photoresist coated semiconductor wafers, MEMS, opto-electronicdevices, photonic devices, flat panel displays, etc) is the completeremoval of aqueous processing, cleaning or rinsing solutions withoutleaving a residue, commonly referred to as a drying watermark. Thesewatermarks result from the concentration of solutes in the aqueousprocessing, cleaning, or drying fluid, as said fluid is dried. In manymicroelectronic, optical, micro-optical, or MEMS structures thiswatermark can negatively impact the manufacturing yield or ultimateperformance of the device. There needs to be an effective method toremove (clean) water-based fluids from surfaces that eliminates theconcentration and ultimate deposition of entrained solutes—eliminatingwatermarks.

One such challenge comes in the manufacturing of MEM's devices.Wet-processing steps generally culminate with a rinse and dry step.Evaporative drying causes water with low levels of solutes that ispooled on the surface and in various micro-features to concentrate inlocations that maximize the surface area of the pool. As a result, thesedrying steps can lead to the concentration of once dissolved solutes inclose proximity to or on motive parts. The deposited materials which canbe organic or inorganic in nature contribute to stiction, the locking ofthe motive part such that it cannot be actuated. “Release stiction” asit is termed during the manufacturing step results, is believed to bederived from adhesive and Van der Waals forces and friction. The forcesgenerated by this phenomenon can completely incapacitate motive parts onMEM's devices.

To combat stiction manufacturers of MEM's devices use solvents such assmall chain alcohols that reduce surface tension during the rinse stepand facilitate a more even drying process. However, these steps alonehave not eliminated the occurrence of stiction. Supercritical CO₂ hasbeen proposed for drying microstructures, (see Gregory T. Mulhern“Supercritical Carbon Dioxide Drying of Micro Structures”) where surfacetension forces can cause damage. Researchers at Texas Instruments Inc.among others (see, e.g., U.S. Pat. No. 6,024,801) have demonstrated thatsupercritical CO₂ can be used to clean organic and inorganiccontaminants from MEM's devices prior to a pacification step, thuslimiting stiction.

These technologies utilizing supercritical CO₂ do not limit stiction bycombination of drying and cleaning where water and solutes are removedsimultaneously so to avoid the concentration of water and solutes atspecific site. Technologies are needed that can prevent release stictionthrough an integrated process of drying, cleaning, and surfacepacification.

Other examples of drying and cleaning challenges related to aqueouswet-processing steps come in the formation of deep vias for interlayermetalization in the production of integrated circuits. These vias,formed by methods known to those familiar with the art, typically havelarge critical aspect ratios creating geometries that can be difficultto clean residues from. Furthermore, wet-processing steps and rinseswith traditional fluids such as water leave once dissolved solutesbehind upon evaporative drying. These solutes deposited at the bottom ofthe vias can inhibit conduction upon metalization lowering functionalyields.

Technologies are needed that remove water (dry) and dissolved solutes(clean) from vias after wet processing steps, thus reducing yieldlosses.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method of cleaning amicroelectronic device, to remove soluble material, particulate matter,and/or contaminants, etc. The method comprises the steps of: providing asubstrate having a surface portion to be cleaned, providing a densifiedcarbon dioxide cleaning composition, the composition comprising carbondioxide and, optionally but preferably a cleaning adjunct, the cleaningadjunct selected from the group consisting of cosolvents, surfactants,and combinations thereof; immersing the surface portion in the densifiedcarbon dioxide composition to thereby clean the surface portion; andthen removing said cleaning composition from the surface portion.

The immersing/cleaning step described above is preferably carried outwith cyclical phase modulation, as explained in greater detail below,during some or all of that step.

Examples of devices that may be cleaned by the present inventioninclude, but are not limited to, microelectromechanical devices (MEMs),optoelectronic devices, and resist-coated substrates.

In a preferred embodiment, process parameters are preferably controlledso that the drying and cleaning composition is maintained as ahomogeneous composition during the immersing step, the removing step, orboth the immersing and removing step, without substantial deposition ofthe drying adjunct or the aqueous entrained solutes on the resistcoating, the patterned feature, or the mechanical, electrical, oroptical components of the device or circuit.

The resist typically comprises a polymeric material, and may be apositive-acting resist or a negative-acting resist. The resist may bepatterned or unpatterned, developed or undeveloped at the time thedrying process is carried out.

The present invention is explained in greater detail in the drawings andspecification set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a substrate having a patterned resist layer formed thereon,with water present in various locations thereon.

FIG. 2 schematically illustrates an apparatus for carrying out themethods of the present invention.

FIG. 3 depicts a phase diagram of predominantly CO₂ system representingthe plausability of a transition from a predominantly CO₂ supercriticalmixture to a gas avoiding a liquid phase.

FIG. 4 schematically illustrates an apparatus for carrying out themethods of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The cleaning step is preferably carried out with cyclical phasemodulation (CPM), or while cyclically modulating/changing the phase ofthe cleaning composition (i.e., cyclically changing the phase of thecleaning composition from liquid to gas, liquid to supercritical,supercritical to gas, supercritical to liquid, etc.). CPM employsprocessing controls of the CO₂ dense phase/cleaning composition thatresult in (1) enhanced physical and (2) enhanced chemical action onresists, resist residues, organic residues, particulate matter, and thelike. With respect to 1), liquid and supercritical CO₂ plasticizeorganic polymers whereby CO₂ permeates the bulk phase at a molecularlevel, augmenting intra- and inter-molecular bonding interactions.During CPM, as the density of the fluid is modulated up and down, carbondioxide mass diffuses in and back out of the polymer bulk phase. Thisprocess causes mechanical stresses and strains on the bulk polymer thatfacilitate expansion, contraction, delamination, potentiallydissolution, and ultimately removal of polymeric materials fromsurfaces. Since dense carbon dioxide cleaning is preferably enhancedusing co-solvents, surfactants, reactants, and sometimes water, thedense phase must also be a good carrier for these materials. Withrespect to 2), CPM is used to control the partitioning of chemicaladjuncts in A) the continuous phase, B) at the surface of the substrate,and C) in the bulk-phase of the material to be removed, such as theresist residue.

Many organic materials are soluble in liquid and/or supercritical CO₂under ranges of conditions of temperature (T) and pressure (P),otherwise noted as continuous-phase density. Solubility of materials inthese ranges is also concentration dependent. Water along with highlypolar low vapor pressure materials, and inorganic materials aretypically insoluble in liquid and supercritical CO₂. However,surfactants with CO₂-philic character have been shown to be very usefulin dispersing and emulsifying these materials in dense CO₂. Furthermore,conventional surfactants that do not contain fluorinated orsiloxane-based components have been shown to to be useful in dense phaseCO2 when combined with certain co-solvent modifiers. During CPM, as thedensity of the continuous phase modulates, chemical adjuncts dissolved,dispersed, or emulsified therein partition between the continuous phaseand the surface of the substrate. Furthermore, CO₂ plus adjuncts in thebulk phase of polymeric and porous residues can, as a result of CPM,diffuse out of bulk materials at different rates, concentrating theadjuncts in the bulk phase. This concentrating effect in the bulk phasekinetically enhances swelling and dissolution of residues. For example,consider the case of an organic polymer residue that contains polarhydrogen bonding functional groups that inhibit swelling and dissolutionin dense CO₂. A soluble hydrogen bonding co-solvent can be employed withCO₂ to enhance the swelling of the bulk polymer and ultimately theremoval of the materials from a substrate. However, the swelling anddissolution or dispersion of this material is limited kinetically by theconcentration of the adjunct in CO2. With CPM, conditions of (T) and (P)can be manipulated to cause partitioning between the continuous phaseand the surface of the wafer, and in the bulk phase of the residue. Thisprocess increases the localized concentration of adjuncts in and onresidues at a molecular level. This concentrating effect, represents andkinetic advantage over solutions, dispersions, or emulsion of adjunctsin dense CO2.

In summary, CPM with dense phase carbon dioxide and chemical adjuncts,enhances the removal of resists, resists residues, particulate, andorganic materials by enhancing physical and chemical action on thesematerials encountered during the manufacturing of microelectronicsubstrates.

Examples of devices that may be cleaned by the present inventioninclude, but are not limited to, microelectromechanical devices (MEMs),optoelectronic devices, and resist-coated substrates.

Any suitable resist composition can be used to carry out the presentinvention, including but not limited to those described in U.S. Pat.Nos. 6,042,997; 5,866,304; 5,492,793; 5,443,690; 5,071,730; 4,980,264;and 4,491,628. Applicants specifically intend that the disclosures ofall United States patent references that are cited herein beincorporated herein by reference in their entirety.

The resist compositions may be applied to the substrate as a liquidcompositions in accordance with generally known procedures, such as byspinning, dipping, roller coating or other conventional coatingtechnique. When spin coating, the solids content of the coating solutioncan be adjusted to provide a desired film thickness based upon thespecific spinning equipment utilized, the viscosity of the solution, thespeed of the spinner and the amount of time allowed for spinning.

The resist compositions are suitably applied to substratesconventionally used in processes involving coating with photoresists.For example, the composition may be applied over silicon wafers (thatmay include one or more layers thereon such as silicon dioxide, siliconnitride, polysiloxand and/or metal, etc.) for the production ofmicroprocessors and other integrated circuit components.Aluminum-aluminum oxide, gallium arsenide, ceramic, quartz or coppersubstrates also may be employed. Substrates used for liquid crystaldisplay and other flat panel display applications are also suitablyemployed, e.g. glass substrates, indium tin oxide coated substrates andthe like.

Following coating of the photoresist onto a surface, it is dried byheating to remove the solvent until preferably the photoresist coatingis tack free. Alternatively it may be dried by the procedures describedherein. Thereafter, it is imaged in a conventional manner. The exposureis sufficient to effectively activate the photoactive component of thephotoresist system to produce a patterned image in the resist coatinglayer.

Following exposure, the film layer of the composition may be baked.Thereafter, the film is developed by contacting the film resist layer toany suitable developer solution (the choice of which will depend in partupon the particular choice of resist material). For example, thedeveloper may be a polar developer, for example an aqueous baseddeveloper such as an inorganic alkali exemplified by sodium hydroxide,potassium hydroxide, sodium carbonate, sodium bicarbonate, sodiumsilicate, sodium metasilicate; quaternary ammonium hydroxide solutionssuch as a tetra-alkyl ammonium hydroxide solution; various aminesolutions such as ethyl amine, n-propyl amine, diethyl amine,di-n-propyl amine, triethyl amine, or methyldiethyl amine; alcoholamines such as diethanol amine or triethanol amine; cyclic amines suchas pyrrole, pyridine, etc. In general, development is in accordance withart recognized procedures. After development the resist is optionallyrinsed (for example with an aqueous rinse) and is then dried, preferablyby the drying procedures described herein.

Following development of the photoresist coating over the substrate, thedeveloped substrate may be selectively processed on those areas bared ofresist, for example by chemically etching or depositing on substrateareas bared of resist in accordance with procedures known in the art.For the manufacture of microelectronic substrates, e.g., the manufactureof silicon dioxide wafers, suitable etchants include a gas etchant, e.g.a chlorine or fluorine-based etchant such a CF₄ or CF₄/CHF₃ etchantapplied as a plasma stream, in accordance with known techniques.

Carbon-dioxide cleaning drying compositions used to carry out thepresent invention typically comprise:

(a) carbon dioxide to balance, typically at least 20, 30, 40, 50 or 60percent;

(b) from 0, 0.01, 0.1, 0.5, 1 or 2 percent to 5 or 10 percent or more ofsurfactant;

(c) from 0, 0.01, 0.1, 1 or 2 to 30, 40 or 50 percent or more of anorganic co-solvent; and

(d) optionally, from 0, 0.01, or 0.1 to 2 or 5 percent water.

Preferably at least one of the surfactant and/or the co-solvent isincluded (e.g., by at least 0.01 percent) in the cleaning/dryingcomposition, and optionally both a surfactant and a co-solvent may beincluded in the composition. Water may or may not be included in thecomposition, depending upon the particular cleaning application and thenature of the substrate. Percentages herein are expressed as percentagesby weight unless otherwise indicated.

The cleaning/drying composition may be provided as a liquid orsupercritical fluid, including cryogenic liquids. Liquid andsupercritical carbon dioxide are herein together referred to as“densified” carbon dioxide in accordance with established usage.

The organic co-solvent may be one compound or a mixture of two or moreingredients The organic co-solvent may be or comprise an alcohol(including diols, triols, etc.), ether, amine, ketone, carbonate, oralkanes, or hydrocarbon (aliphatic or aromatic) The organic co-solventmay be a mixture of compounds, such as mixtures of alkanes as givenabove, or mixtures of one or more alkanes in combination with additionalcompounds such as one or more alcohols as described above. (e.g., from 0or 0.1 to 5% of a C1 to C15 alcohol (including diols, triols, etc.)).Any surfactant can be used to carry out the present invention, includingboth surfactants that contain a CO₂-philic group (such as described inPCT Application WO96/27704) linked to a CO₂-phobic group (e.g., alipophilic group) and surfactants that do not contain a CO₂-philic group(i.e., surfactants that comprise a hydrophilic group linked to ahydrophobic (typically lipophilic) group). A single surfactant may beused, or a combination of surfactants may be used. Numerous surfactantsare known to those skilled in the art. See, e.g., McCutcheon's Volume 1:Emulsifiers & Detergents (1995 North American Edition) (MC PublishingCo., 175 Rock Road, Glen Rock, N.J. 07452). Examples of the majorsurfactant types that can be used to carry out the present inventioninclude the: alcohols, alkanolamides, alkanolamines, alkylarylsulfonates, alkylaryl sulfonic acids, alkylbenzenes, amine acetates,amine oxides, amines, sulfonated amines and amides, betaine derivatives,block polymers, carboxylated alcohol or alkylphenol ethoxylates,carboxylic acids and fatty acids, a diphenyl sulfonate derivatives,ethoxylated alcohols, ethoxylated alkylphenols, ethoxylated aminesand/or amides, ethoxylated fatty acids, ethoxylated fatty esters andoils, fatty esters, fluorocarbon-based surfactants, glycerol esters,glycol esters, hetocyclic-type products, imidazolines and imidazolinederivatives, isethionates, lanolin-based derivatives, lecithin andlecithin derivatives, lignin and lignin derivatives, maleic or succinicanhydrides, methyl esters, monoglycerides and derivatives, olefinsulfonates, phosphate esters, phosphorous organic derivatives,polyethylene glycols, polymeric (polysaccharides, acrylic acid, andacrylamide) surfactants, propoxylated and ethoxylated fatty acidsalcohols or alkyl phenols, protein-based surfactants, quaternarysurfactants, sarcosine derivatives, silicone-based surfactants, soaps,sorbitan derivatives, sucrose and glucose esters and derivatives,sulfates and sulfonates of oils and fatty acids, sulfates and sulfonatesethoxylated alkylphenols, sulfates of alcohols, sulfates of ethoxylatedalcohols, sulfates of fatty esters, sulfonates of benzene, cumene,toluene and xylene, sulfonates of condensed naphthalenes, sulfonates ofdodecyl and tridecylbenzenes, sulfonates of naphthalene and alkylnaphthalene, sulfonates of petroleum, sulfosuccinamates, sulfosuccinatesand derivatives, taurates, thio and mercapto derivatives, tridecyl anddodecyl benzene sulfonic acids, etc.

FIG. 1 illustrates a resist-coated substrate article 10 to be dried bythe method of the present invention. The article comprises a substrate11, which may comprise silicon or any other suitable material asdescribed above, and which may itself comprise one or more layers,having a resist coating 12 formed thereon. Water droplets 14, 15, to beremoved by drying, are on the top surface and in a trench formed in theresist coating.

FIG. 2 schematically illustrates an apparatus for carrying out themethod of the invention. The apparatus comprises an enclosed dryingvessel 21, suitable for containing liquid or supercritical carbondioxide, in which vessel the coated substrate 10 (or othermicroelectronic device to be cleaned) is positioned on a suitablesupport 27. The drying vessel may include a door, a stirring device orother means of agitation, a view window, a compressor connected to thedrying vessel to increase or decrease the pressure therein, a heatexchanger, heater or cooler connected to the drying vessel to increaseor decrease the temperature of the contents thereof, etc.

A carbon dioxide cleaning/drying composition supply 22 is connected tothe drying vessel by appropriate piping. The cleaning/drying compositionsupply 22 may itself comprise one or more storage vessels, pumps,valves, piping for mixing the drying adjunct into the carbon dioxide,etc. The vessel may be filled with the cleaning/drying composition to alevel 28 above the article to be cleaned 10.

Depending upon the particular technique or combination of techniquesbeing employed to control the processing conditions, the system includesa supply of a second gas, second material, and/or additional carbondioxide 24 connected to the drying vessel 21.

If desired, a developer solution supply 25 may be connected to thevessel so that both development and drying of the substrate may becarried out in the same vessel 21.

A draining system 26 is preferably connected to the vessel 21 fordraining whatever composition is contained therein. The draining systemmay itself comprise appropriate pumps, valves, compressors and the like(some of which components may be serve multiple functions in conjunctionwith supply elements described above), may include a still fordistilling and optionally recycling ingredients such as carbon dioxide,and may include suitable piping, valves, etc. for recycling variouscompositions or constituents thereof to supply elements for re-use. Forexample, used drying composition may be distilled to allow carbondioxide to be recycled and re-used as part of the drying composition, orto the source of additional carbon dioxide supply.

As noted above, the method of the invention comprises the steps of:

(a) providing a substrate having a an imaged or patterned feature suchas a resist coated silicon wafer and having water on the resist coating;

(b) providing a densified (e.g., liquid or supercritical) carbon dioxidedrying composition, the drying composition comprising carbon dioxide anda drying adjunct, the drying adjunct selected from the group consistingof cosolvents, surfactants, and combinations thereof;

(c) immersing the surface portion in the densified carbon dioxide dryingcomposition; and then

(d) removing the drying composition from the surface portion.

The process parameters may be controlled so that the drying compositionis maintained as a homogeneous composition during the immersing step,the removing step, or both the immersing and removing step, withoutsubstantial deposition or redeposition of the drying adjunct orcontaminants on the resist coating.

Preferably, the providing step is carried out by mixing the carbondioxide with the adjunct to produce a homogeneous solution, and then theimmersing step is carried out while maintaining the drying compositionas a homogeneous solution. Such mixing can be carried out in the dryingcomposition supply 22 by any suitable means, such as stirring, injectionunder pressure, etc.

The removing step is preferably carried out while maintaining the dryingcomposition as a homogeneous solution. In general, this is achieved byinhibiting the boiling of the drying composition as it is drained fromthe drying vessel. When draining liquid CO₂ from a vessel the liquidreaches a state where it is at equilibrium with CO₂ vapor, termedsaturated vapor pressure. To maintain saturation, as liquid is removedfrom the vessel by venting or pumping preferably from the bottom of thevessel, the liquid phase boils to generate vapor for the increasingvolume of the vapor phase. This boiling which may be nucleated atliquid/gas, and liquid/solid interfaces causes adjuncts with lower vaporpressure than CO₂ including, co-solvents and surfactants, and solutecontaminants to concentrate at interfaces. Concentrated adjuncts,deposited contaminants and interfacial stresses created by boiling atliquid/solid interfaces can be damaging to resist features, MEM's, orother patterned microdevices. In the case of imaged and developedresists, feature sizes less 130-nmwith aspect ratios greater than 3 areparticularly susceptible to damage. Process controls to prevent suchdamage are as follows.

For example, when the drying composition is a liquid drying composition,the removing step may be carried out by pressurizing the enclosedchamber with a second compressed gas (e.g., helium, nitrogen, air,mixtures thereof) from supply 24 by an amount sufficient to inhibitboiling of the drying composition during the draining step. The secondgas is preferably one that is substantially immiscible in the dryingcomposition possessing a saturated vapor pressure that is higher thanCO₂. The second gas may be used to itself force the drying compositionfrom the vessel, or the drying composition may be pumped or otherwisedrained from the vessel while the second gas maintains anover-pressurization at the gas-liquid interface formed in the washvessel during draining thereof.

Alternatively, if the drying composition is in the liquid phase, thedraining step can be accomplished without boiling by liquid-gasequilibration with a secondary chamber or storage vessel. In thisscenario, drying chamber 21 is connected to storage vessel 31 bygas-side line 32 (top), and liquid-side line 33. Each line contains avalve 34, 35 to separate or isolate vessels 21 and 31 from one another.During the draining step, storage vessel 31 contains a liquid CO₂composition at a saturated pressure equal to or in excess of thesaturated vapor pressure in the cleaning/drying vessel 21. Draining maybe accomplished by first opening the gas-side connection 32 betweenvessels 21 and 31, and then opening the liquid-side connection 33.Liquid flows from cleaning vessel 21 to storage vessel 31 by gravity, if21 is located sufficiently above 31, amd/or by pumping. Liquid transferdescribed above avoids boiling thereby avoiding potential damage toresist features or other device features.

When the drying composition is a supercritical drying composition therewill not be a gas-liquid interface. In this case, the removing step maybe carried out by first adding a second material (e.g., a cosolvent asdescribed above or a secondary gas) to the supercritical dryingcomposition so that it is converted to a liquid drying composition,which can then be removed from the vessel as described above. If asecondary gas is used to cause the supercritical fluid phase to changeto a liquid, the gas should be chosen from those having a saturatedvapor pressure that is higher than that of CO₂ and/or a criticalpressure and temperature higher than that of CO₂. Exemplary gasesinclude but are not limited to: nitrogen, argon, helium, oxygen, andmixtures thereof.

Alternatively, when the drying composition is in the supercriticalstate, the adjunct containing fluid can be sufficiently diluted prior tothe draining step by simultaneous addition of pure supercritical CO₂ andremoval of adjunct-containing supercritical CO₂. After sufficient fluidturnover is accomplished and adjunct concentration is effectivelyminimized, the supercritical fluid is vented from the drying vessel bymaintaining the fluid in the supercritical state until a transition ismade directly to the gas state thus avoiding the liquid state. This isaccomplished during the draining/venting step by maintaining the fluidtemperature above the critical temperature of the mixture (Tc) until thepressure in the vessel is below the critical pressure of the mixture(Pc). FIG. 3 depicts a phase diagram of predominantly CO₂ systemrepresenting the plausibility of a transition from a predominantly CO₂supercritical mixture to a gas avoiding a liquid phase. Because theexpansion of the supercritical fluid and subsequent expansion of theremaining gas is an endothermic process, heat may need to be added tothe system to maintain the temperature of the fluid or gas above thecritical temperature thus avoiding condensation of the supercriticalfluid or gas to a liquid or solid. By effecting a direct transition fromthe supercritical phase to the gas phase, liquid boiling is avoidedthereby avoiding the interfacial stress caused by a retracting liquidmeniscus at the liquid/solid interface, and unwanted deposition ofsolutes onto and in microstructures.

In another embodiment, the removing step is carried out by diluting thedrying composition with additional carbon dioxide from supply 24, duringwhich dilution the drying composition is removed from the vessel bydraining system 23. Since larger quantities of carbon dioxide arerequired for such a technique, the use of a still to distill drainedcarbon dioxide, along with appropriate piping and valving for returningthe carbon dioxide to supply 22 or supply 24 for subsequent re-use, ispreferred.

In still another embodiment, a secondary gas is used, at a pressurerange above the saturation point of CO₂ gas, to displace liquid andgaseous CO₂ in the drying chamber leaving a predominance of thesecondary gas in the vapor phase. The secondary gas, possessing a lowerheat of compression, can be vented from the chamber to ambient pressurewith less heat loss to the system. Also represented by a smallerJoule-Thomson coefficient, (μ), the expansion of the gas from highpressure to atmospheric conditions results in less change in temperatureat or in close proximity to the substrate. (μ_(CO2)>μ_(x), whereX=secondary gas).

μ=(dT/dP)_(H)

In this embodiment, the secondary gas is useful in avoiding thermalshock when rapid cycling of pressure is desired for high throughput.Substrates such as silicon wafers can crack or become damage whensignificant temperature gradients exist in that substrate. Cooling ofchambers and vessels from gaseous expansion can also add valuableprocessing time and require substantial heat input for temperatureregulation. The use of a secondary gas can minimize heat loss and heatinputs, potentially reducing cycle time and energy requirements.

Cyclical Phase Modulation (CPM) during an example wafer cleaningprocess. During the manufacturing of an integrated circuit, asemiconductor wafer is cleaned after an etch step in the followingprocess, FIG. 4, using dense phase carbon dioxide. Dense carbon dioxideis stored in pressure vessel (I) (50) at conditions of between 300 and5000 psi and a temperature of between −20° C. and 100° C., furtherdescribed as the high-pressure vessel. A wafer is loaded into cleaningchamber (III) (51) in an automated or manual fashion where the wafer isheld on a platform (XI) (52) connected to a chuck and a sealed shaft(not shown) so that the platform can spin. Located above the wafer heldon the platform is a spray bar (X) (53) designed to disperse the flow ofdense phase carbon dioxide and chemical adjuncts and to directsubstantial fluid action onto the surfaces of the wafer. Cleaningchamber (III) is pressurized with clean carbon dioxide from either abulk storage tank (XII) (54) through valve (i) (55) or from pressurevessel (I) (50) through valve (a) (56) to a pressure of between 300 psiand 5000 psi at a temperature of between −20° C. and 100° C. Thetemperature of the dense CO₂ can be modulated using heat exchanger (II)(60). Additionally, the temperature of the processing phase in chamber(III) (51) can be modulated using heat exchangers internal or externalto the chamber. Highly filtered chemical adjuncts as required are addedto cleaning chamber (III) (51) from adjunct addition module (VI) (61)through valve (b) (62) during the addition of dense CO₂ or alternativelyprior to the addition of the dense CO₂. The adjunct addition moduleserves to store, filter, mix and sequentially or simultaneously meteradjunct materials to the cleaning chamber. During the cleaning process,the dense phase CO₂ is optionally circulated from the cleaning chamberthrough valve (e) (66) using pump (VII) (63) through solid separationfilter (VIII) (64) and valve (f) (65) back into the chamber through thespray bar (X) (53). During the circulation the wafer can be spun atrates between zero and 3000 rpm. Also during the cleaning step, thedensity of the system is cyclically modulated. This can be accomplishedwith the following sequence. Pressure vessel (I) (50), the high-pressurevessel, containing dense CO₂, is maintained at a pressure notably above(50 to 2000 psi greater than) that of cleaning chamber (III) (51).Pressure vessel (V) (70), low-pressure vessel, is held at a pressurenotably less than (50 to 3000 psi lower than) cleaning chamber (III)(51), and the temperature of the independent vessels are roughly thesame. In the cyclical process, valve (a) (56) is first opened to allowfor the flow of mass between (I) and (III) then closed. Valve (d) (71)is then opened to allow for the flow of mass between (III) and (V).Valve (g) (72) is then opened to separator/abatement module (IX) (73)such as a filter or other separator that serves to separate chemicaladjuncts from CO₂ and removed waste. The abatement module also allowsfor removed CO₂ mass to be re-added to tank (I) through valve (h) (74)completing the mass flow cycle. Alternatively, CO₂ mass can be added topressure vessel (I) from bulk storage, to reestablish higher pressure invessel (I) than chamber (III). This mass flow cycle is repeated multipletimes (between 1 and 500) in a given cleaning cycle resulting incyclical phase modulation (CPM). Dense CO₂ circulation in cleaningchamber (III) can optionally be augmented using pump (VII) and valves(e) and (f) during CPM. During the cleaning step, CPM can bealternatively achieved using variable volume chamber (IV) (80) withvalve (c) (81) opened. In this scenario, the volume of (IV) is increasedand reduced cyclically, between 1 and 500 times in a given cleaningcycle. In this CPM scenario, fluid can optionally be circulated throughthe cleaning chamber (III) using pump (VII) and valves (e) and (f).After a period sufficient to remove the contaminants from the surface ofthe wafer, dense phase CO₂ mixture is flushed from the system throughvalve (d) into vessel (V) with addition of pure dense phase CO₂ fromtank (I) through valve (a). This rinse process continues until alladjunct and waste are removed from the chamber. The dense CO₂ is ventedfrom cleaning chamber (III) to a waste or abatement system.

The present invention is explained in greater detail in the followingnon-limiting Examples

COMPARATIVE EXAMPLE A Treatment of a Coated Wafer with Liquid CarbonDioxide

A CO₂-miscible, hydrophilic solvent, such as isopropanol (IPA), wasadded to a high-pressure vessel that contained a piece of apoly(hydroxystyrene) (PHS) coated silicon wafer. Liquid CO₂ was added tothe high-pressure vessel. As the liquid CO₂/IPA (2% IPA by volume)mixture meniscus level rose above the surface of the wafer, damage tothe wafer was observed. After the system was mixed for 15 minutes, theliquid CO₂/IPA mixture was drained from the bottom of the high-pressurevessel. More damage to the wafer was observed as the IPA boiled at theliquid/gas/wafer interface.

EXAMPLE 1

Treatment of a Coated Wafer with Liquid Carbon Dioxide

Liquid CO₂ was added to a high-pressure vessel that contained a piece ofa PHS coated silicon wafer until the wafer was completely submerged inliquid CO₂. A mixture that contained liquid CO₂ and IPA, 2% IPA byvolume, (alternatively any CO₂-miscible, hydrophilic solvent, or anyhydrophilic/CO₂-philic surfactant) was added to the high-pressure vesselthat contained the piece of PHS coated silicon wafer submerged in liquidCO₂. No damage to the wafer was observed. The system was mixed for 15minutes. There was still no damage to the wafer. A secondary gas (heliumor nitrogen) was added to the top of the high-pressure vessel. Theliquid CO₂/IPA mixture was drained under the pressure of the secondarygas to prevent boiling at the liquid/gas/wafer interface. There was nodamage to the wafer after the system was drained with a secondary gas.The system was rinsed with pure liquid CO₂ and was then drained asmentioned above. There was no damage to the wafer.

EXAMPLE 2 Treatment of a Coated Wafer with Liquid Carbon Dioxide

Liquid CO₂ at its saturated vapor pressure was added to a high-pressurevessel that contained a piece of a PHS coated silicon wafer until thewafer was completely submerged in liquid CO₂. A mixture that containedliquid CO₂ and IPA, 2% IPA by volume, (alternatively any CO₂-miscible,hydrophilic solvent, or hydrophilic/CO₂-philic surfactant) was added tothe high-pressure vessel that contained the piece of PHS coated siliconwafer submerged in liquid CO₂. No damage to the wafer was observed. Theliquid CO₂ mixture was drained from the high-pressure vessel to anotherhigh-pressure vessel containing predominantly liquid CO₂ at saturatedvapor pressure by first opening a valve connecting the vapor side ofboth vessels then by opening a valve connecting the liquid side of bothvessels. The liquid was drained by force of gravity as the first vesselwas positioned substantially above the second to allow for completedrainage. No damage was observed. Pure liquid CO₂ was added to thevessel containing the wafer segment as a rinse, and that liquid wassubsequently drained in the manor described above. Again, no damage wasobserved.

EXAMPLE 3 Treatment of a Coated Wafer with Liquid and Supercritical CO₂

Liquid CO₂ was added to a high-pressure vessel that contained a piece ofa PHS coated silicon wafer until the wafer was completely submerged inliquid CO₂. A mixture that contained liquid CO₂ and IPA, 2% IPA byvolume, (alternatively any CO₂-miscible, hydrophilic solvent orsurfactant that increased the carry capacity of CO₂ for water) was addedto the high-pressure vessel that contained the piece of PHS coatedsilicon wafer submerged in liquid CO₂. No damage to the wafer wasobserved. After a period of time sufficient to remove the substantialmajority of the water from the surface of the wafer, the liquid mixturewas diluted with pure liquid CO₂ to effect approximately 5 liquidturnovers in the drying chamber. Heat was then added to the liquid CO₂causing a transition to the supercritical phase. The chamber containingthe wafer is then drained and vented by maintaining the temperature offluid and gas above the critical temperature of CO₂, thus avoiding theliquid phase. The wafer was removed from the chamber with no damage.

EXAMPLE 4 Treatment of a Coated Wafer with Supercritical Carbon Dioxide

Supercritical CO₂ was added to a high-pressure vessel that contained apiece of a PHS coated silicon wafer. A mixture that containedsupercritical CO₂ and IPA, 2% IPA by volume, (alternatively anyCO₂-miscible, hydrophilic solvent or surfactant that increased the carrycapacity of CO₂ for water) was added to the high-pressure vessel thatcontained the piece of PHS coated silicon wafer and supercritical CO₂.No damage to the wafer was observed. The system was mixed for 15minutes. There was still no damage to the wafer. A secondary gas (heliumor nitrogen) was added to the top of the high-pressure vessel until thesystem became subcritical and a liquid meniscus was formed. The liquidCO₂/IPA mixture was drained under the pressure of the secondary gas toprevent boiling at the liquid/gas/wafer interface. There was no damageto the wafer after the system was drained with a secondary gas. Thesystem was rinsed with pure liquid CO₂ and was then drained as mentionedabove. There was no damage to the wafer.

COMPARATIVE EXAMPLE B Solvation of Water from a Coated Wafer with LiquidCarbon Dioxide

A droplet of water was dripped on top of a piece of a PHS coated siliconwafer. The wafer that contained the water droplet was placed in thehigh-pressure view cell. Pure liquid CO₂ was added to the high-pressurevessel. The system was mixed for 15 minutes. The liquid CO₂ did notsolvate the entire droplet of water as determined visually through asapphire window on the view cell.

EXAMPLE 5 Solvation of Water from a Coated Wafer with Liquid CarbonDioxide and Cosolvent

A droplet of water was dripped on top of a piece of a PHS coated siliconwafer. The wafer that contained the water droplet was placed in thehigh-pressure view cell. Liquid CO₂ was added to a high-pressure vesselthat contained a piece of a PHS coated silicon wafer until the wafer wascompletely submerged in liquid CO₂. A mixture that contained liquid CO₂and IPA, 2% IPA by volume, (alternatively any CO₂-miscible, hydrophilicsolvent) was added to the high-pressure vessel that contained the pieceof PHS coated silicon wafer submerged in liquid CO₂. No damage to thewafer was observed. The system was mixed for 15 minutes. The waterdroplet was completely solvated. There was still no damage to the wafer.A secondary gas (helium or nitrogen) was added to the top of thehigh-pressure vessel. The liquid CO₂/IPA mixture was drained under thepressure of the secondary gas to prevent boiling at the liquid/gas/waferinterface. There was no damage to the wafer after the system was drainedwith a secondary gas. The system was rinsed with pure liquid CO₂ and wasthen drained as mentioned above. There was no damage to the wafer.

EXAMPLE 6 Solvation of Water from a Coated Wafer with Liquid andSupercritical Carbon Dioxide and Cosolvent

A whole 5″ PHS coated wafer wetted with water, as it would be in anaqueous post-development process, was placed in the prototype dryingchamber. The chamber was filled with liquid carbon dioxide. Theprototype system contained a second high pressure vessel, containingliquid CO₂ plus 2% IPA by volume, (alternatively any CO₂-miscible,hydrophilic solvent or surfactant that increased the carry capacity ofCO₂ for water) The mixed liquid CO₂/IPA was added to the drying chamberfrom the second high-pressure vessel using a pump. The system was mixedfor 15 minutes. The liquid CO₂/IPA mixture was flushed with 5 liquidturnovers of pure liquid CO₂ so that the concentration of IPA dropped toa fraction of its previous concentration. There was no meniscusformation during the CO₂ flush. After the CO₂ flush, the liquid CO₂ washeated to 35° C. transitioning the fluid to a supercritical phase. Thesupercritical CO₂ was then drained/vented from the vessel as heat wasadded to maintain the fluid, and subsequently the gas, above thecritical temperature of CO₂. When the chamber was completely vented thewafer was removed dry and undamaged.

EXAMPLE 7 Drying of Water from an Imaged and Aqueously DevelopedResist-Coated Wafer Using CO₂ and Chemical Adjuncts

A 5-inch silicon wafer coated with a PHS photoresist and a PAG wasimaged, developed using 0.238 normal tetramethyl ammonium hydroxide, andrinsed with deionized water. The wet wafer was then transferred to ahigh-pressure drying chamber, where liquid CO₂ at saturated vaporpressure was added in a small amount. Additional liquid CO₂ at saturatedvapor pressure premixed with a hydrophilic/CO₂-philic surfactant wasadded to and circulated through the chamber to displace and remove thewater from the surface of the wafer and features of the resist pattern.After a short period of time the liquid was drained to a secondarystorage vessel containing a small amount of liquid CO₂ first by allowinga vapor-side communication between the two vessels then by opening avalve connecting the bottom of the drying vessel with the bottom of thesecond storage vessel. The second storage vessel was positionsufficiently below the drying chamber that the majority of the liquiddrained from the drying chamber. The drying chamber was then filled withpure liquid CO₂ as a rinse followed by draining as described above. Thiswas repeated to insure that the concentration of the adjunct waseffectively zero. The small amount of remaining liquid CO₂ in the dryingchamber was heated to above its critical point, 35° C., and the CO₂ wasvented while maintaining the fluid/gas temperature above the criticaltemperature thus avoiding the formation of a liquid meniscus. Theimaged, developed, and dried wafer was then removed from the chamber,stored in the absence of light and moisture, and then analyzed using ascanning electron microscope. The micrograph showed that the developedfeatures, demonstrating line/space patterns of less than 120-nm, wereconsistent structurally unaffected by the CO₂ drying process.

EXAMPLE 8 MEM's Water and Contaminant Removal

During the manufacturing of a MBM's device containing a series ofelectrostatic actuators, a sacrificial oxide layer is removed usingaqueous hydrofluoric acid, exposing a series of pivoting plates parallelto the substrate surface. After a sequential rinse step, the device istransferred to a high-pressure CO₂-based drying chamber, where a liquidCO₂ mixture is added at saturated vapor pressure. The liquid CO₂contains a CO₂-philic/hydrophilic surfactant that is premixed with theCO₂ to ensure a homogeneous composition. After a period of circulation,pure liquid CO₂ is fed into the chamber as liquid CO₂, surfactant, waterand entrained solutes are removed from the vessel at constant pressure.The liquid CO₂ remaining in the chamber is then heated to above itscritical temperature converting the fluid into the supercritical state.The supercritical fluid in the processing chamber is then vented into astorage tank serving to ensure that the temperature of the fluid/gasmixture stays above the critical temperature of CO₂. This serves toensure that the liquid state, a liquid meniscus, and associated surfacetension are avoided during the draining/venting step. An SEM analysis ofthe MEM's device shows that the pivoting plates are all substantiallyparallel to the substrate surface with no evidence of release stiction.

EXAMPLE 9 Post CMP Cleaning

Polishing slurry, polishing residues and particulates are removedpost-CMP using the following process steps. The substrate, asemiconductor wafer with a metal or dielectric surface, is loaded into apressure vessel. An aqueous solution of hydrogen peroxide (30%concentration in water) in a liquid CO₂ emulsion containing a highpurity CO₂-philic-b-hydrophilic surfactant is introduced at 1,200 psiand room temperature. Cyclical phase modulation is used to condense theemulsion onto the surface of the wafer followed by re-emulsification.This is accomplished by increasing the effective volume of the cleaningchamber causing a reduction in pressure from 1200 psi at roomtemperature to 790 psi at about 15 C. The volume is increased using anautomated variable volume cylinder and appropriate valves. The aqueouscleaning solution is condensed onto the surface of the wafer for a shortperiod of time as the density of the liquid CO₂ is reduced. The pressureis then increased by a reduction of vessel volume restoring the pressurein the cleaning chamber to 1200 psi. The cycle is repeated 20 times. Thefirst solution is then displaced from the vessel by a second cleaningsolution consisting of an aqueous fluoride in CO₂ emulsion with a highpurity CO₂-philic-b-hydrophilic surfactant. The pressure is thenmodulated cyclically as above, 20 times. Supercritical CO₂ at 1800 psiand 40 C, with a high purity surfactant is then flowed through thevessel to facilitate the removal of any remaining particulates. Asupercritical CO₂ rinse is then completed by addition of pure CO₂ to thevessel. The system is vented a final time and the substrate is removed.

EXAMPLE 10

Polishing slurry, polishing residues and particulates are removedpost-CMP using the following process steps. The substrate, asemiconductor wafer with a metal or dielectric surface, is loaded into apressure vessel. An aqueous solution of hydrogen peroxide in a liquidCO₂ emulsion containing a high purity CO₂-philic-b-hydrophilicsurfactant is introduced at 1,200 psi and room temperature. The aqueouscleaning solution is condensed onto the surface of the wafer for a shortperiod of time using a variable volume chamber connecting to thecleaning vessel. The pressure is then increased by a reduction of vesselvolume to restore the pressure to the original value. The cycle isrepeated 20 times. The first solution is displaced from the vessel by asecond cleaning solution consisting of an aqueous fluoride in CO₂emulsion with a high purity CO₂-philic-b-hydrophilic surfactant. Thepressure is then modulated as above 20 times using a variable volumechamber. Supercritical CO₂ containing a small amount CO₂-solublechelating agent (ethylenediaminetetraacetic acid) is then flowed throughthe vessel to facilitate the removal of any remaining metal ions.Supercritical CO₂ with a high purity surfactant is then flowed throughthe vessel to facilitate the removal of any remaining particulate mater.A supercritical CO₂ rinse is then completed by addition of pure CO₂ tothe vessel. The system is vented a final time and the substrate removed.

EXAMPLE 11

Photoresist is used to pattern substrates for ion implantation. Thephotoresist used for this process is removed in the following steps. Thesubstrate, a semiconductor post ion implantation, is loaded into apressure vessel. Supercritical CO₂ is added to the vessel at 3,000 psiand 35° C. As the supercritical CO₂ circulated through the vessel, aco-solvent mixture consisting of triethanolamine,N-methyl-2-pyrrolidone, a surfactant containing both CO₂-philic andhydrophilic components, and water are added. The mixture composition byweight is 7:2:1:1, and the total concentration of adjunct added is 2.5%w/v of the fluid system. The pressure of the vessel is reduced using avariable volume chamber and appropriate valves causing an expansion ofthe processing fluid in the cleaning chamber and thereby condensing aconcentrated mixture of the adjunct mixture onto the surface of thesubstrate. The temperature of the mixture drops below the T_(c) in thecourse of the expansion causing a transition to liquid CO2. The systemis re-pressurized and the fluid mixture heated above T_(c) again usingthe variable volume chamber and internal heaters. This cycle is repeated20 times and followed by a pure supercritical CO₂ rinse. The system isvented and the substrate removed.

EXAMPLE 12

Polymeric photoresist and resist residue is removed from via structuresof a test wafer after reactive ion etching using the following processsteps. An amine (triethylamine) in supercritical CO₂ plus a high puritysurfactant with both a CO₂-philic and an oleophilic segment is added tothe vessel at 3,000 psi at 60° C. (2% w/v amine, 1% w/v surfactant). Thefluid mixture is circulated through the vessel. The pressure of thefluid mixture is rapidly reduced to 1,500 psi thereby condensing theadjunct onto the surface of the substrate. The pressure is then rapidlyincreased back to 3,000 psi re-dispersing all chemical adjuncts. Thecycle is repeated 20 times using a variable volume chamber. Heat isadded to the chamber using an internal heater to maintain thetemperature as near to 60° C. as possible. Helium gas at 3500 psi wasthen added to the cleaning chamber as a valve at the bottom of thechamber was opened to a waste vessel. The processing fluid was rapidlyflushed from the chamber and replaced by a pressurized atmosphere ofpure helium. After the helium was vented off the cleaning vessel wasrinsed with pure supercritical CO₂ A second cleaning solution consistingof a co-solvent (2,4-pentanedione, 3% w/v total) and a high puritysurfactant (1% w/v) was added to the cleaning vessel with CO₂ at 3000psi and 60 C. The pressure of the system is modulated as described above20 times while the temperature of the fluid is maintained as close to60° C. as possible using an internal heater. The cleaning fluid wasdrained as above using helium as a secondary gas. Finally, a puresupercritical CO₂ rinse is completed, the system was drained usinghelium as a secondary gas and then vented, and the substrate removed.

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. A method of cleaning contaminants from amicroelectronic device, comprising the steps of: providing a substratehaving a surface portion to be cleaned, providing a densified carbondioxide cleaning composition, said cleaning composition comprisingcarbon dioxide and a cleaning adjunct, said cleaning adjunct selectedfrom the group consisting of cosolvents, surfactants, and combinationsthereof; immersing said surface portion in said densified carbon dioxidecleaning composition; and then removing said cleaning composition fromsaid surface portion; wherein the phase of said cleaning compositioncyclically modulated during at least a portion of said immersing step.2. The method according to claim 1, wherein said densified cleaningcomposition is a liquid and is at saturated vapor pressure, and saidremoving step is carried out by draining said liquid with vapor sidecommunication between said cleaning chamber and a receiving vessel. 3.The method according to claim 1, further comprising: maintaining saidcleaning composition as a homogeneous composition during at least one ofsaid immersing step and said removing step.
 4. The method according toclaim 1, wherein said microelectronic device comprises amicroelectromechanical device.
 5. The method according to claim 1,wherein said microelectronic device comprises an optoelectronic device.6. The method according to claim 1, wherein said microelectronic devicecomprises a resist-coated substrate.
 7. The method according to claim 1,wherein said carbon dioxide is supercritical carbon dioxide.
 8. Themethod according to claim 1, wherein said cleaning adjunct comprises aco-solvent.
 9. The method according to claim 1, wherein said cleaningadjunct comprises a surfactant.
 10. The method according to claim 1,wherein said providing step is carried out by mixing said carbon dioxidewith said adjunct to produce a homogeneous solution.
 11. The methodaccording to claim 1, wherein said cleaning composition is a liquidcleaning composition, wherein said immersing and removing steps arecarried out in an enclosed chamber, and wherein said removing step iscarried out by pressurizing said enclosed chamber with a secondcompressed gas by an amount sufficient to inhibit boiling of said dryingcomposition.
 12. The method according to claim 1, wherein said cleaningcomposition is a supercritical cleaning composition, wherein saidimmersing and removing steps are carried out in an enclosed chamber, andwherein said removing step is carried out by adding a second material tosaid supercritical cleaning composition so that it is converted to aliquid cleaning composition.
 13. The method according to claim 1,wherein said removing step is carried out by diluting said cleaningcomposition with additional carbon dioxide.
 14. A method according toclaim 1, wherein said cleaning comprises removal of water from saiddevice.
 15. A method of cleaning contaminants from a microelectronicdevice, comprising the steps of: providing a substrate having a surfaceportion to be cleaned; providing a densified carbon dioxide cleaningcomposition, said cleaning composition comprising carbon dioxide and acleaning adjunct, said cleaning adjunct selected from the groupconsisting of cosolvents, surfactants, and combinations thereof;immersing said surface portion in said densified carbon dioxide cleaningcomposition for a time sufficient to remove at least a portion of saidsolid particulates from said surface portion; and then removing saidcleaning composition from said surface portion, wherein said removingstep is carried out while inhibiting redeposition of contaminants onsaid surface portion; wherein the phase of said cleaning compositioncyclically modulated during at least a portion of said immersing step.16. The method according to claim 15, wherein said densified carbondioxide cleaning composition is a supercritical fluid, and saidinhibiting step is carried out by: introducing a clean secondary gasinto said supercritical fluid cleaning composition; and removing saidsupercritical fluid from said surface portion under pressure from saidsecondary gas.
 17. The method according to claim 15, wherein saiddensified carbon dioxide cleaning composition is a supercritical fluid,and said inhibiting step is carried out by: introducing clean heatedsupercritical CO₂ into said supercritical fluid cleaning composition;and removing said supercritical fluid from said surface portion underpressure from said heated supercritical CO₂.
 18. The method according toclaim 15, wherein said densified carbon dioxide cleaning composition isa liquid, and said inhibiting step is carried out by: introducing aclean secondary gas into said liquid cleaning composition; and removingsaid liquid cleaning composition from said surface portion underpressure from said secondary gas.
 19. The method according to claim 15,wherein said densified carbon dioxide cleaning composition is a liquid,and said inhibiting step is carried out by: introducing clean heated gasor supercritical CO₂ into said supercritical fluid cleaning composition;and removing said liquid cleaning composition from said surface portionunder pressure from said heated gas or supercritical CO₂.
 20. A methodaccording to claim 15, wherein said cleaning step is initiated with saidcleaning composition in a liquid state, and after a period of time saidinhibiting step is carried out by diluting said composition with pureliquid CO₂ and then heating said composition produce a supercriticalfluid, followed by removing said supercritical fluid while maintainingthe temperature of the fluid and gas above the critical temperature ofCO₂.